XPS 9350 stuck booting

My sister in law has an XPS 13 9350 that decided to stop booting for no reason...

When turning it on, it's stuck at the DELL windows booting screen (animated circle dots spinning around). It'll sit like this for many minutes, then eventually reboot and start over.

Tried running the diagnostics from the F12 menu. Comes back clean. Haven't been able to get it to boot a safe mode or rescue mode.

I've also tried booting a Windows 10 USB installer stick.. but that also failed. It also got stuck on the spinning circle of dots, but with the windows 10 logo in the middle, and corrupted dell logo graphics...

Any ideas?booting win10 USB